Metalizing material

ABSTRACT

A metallizing composition for forming electrically conductive areas on dielectric materials, which areas bond securely to the dielectric base materials, and which areas form secure bonds with conductive and mechanical attachments, the composition being a mixture by weight of approximately 63.7 percent gold, 32.3 percent palladium, 4.0 percent silver.

United States Patent References Cited lnventor Sandlord S. Cole, Jr. [56] West Caldwell, NJ. UNITED STATES PATENTS Q J' $53 2,950,995 8/1960 Place, Sr. etal. 117/227 t d L 1971 2,950,996 8/1960 Place, Sr. etal. 1 17/227 23 AIS! M'mmnc 3,149,002 9/1964 Place, Sr. et al. 117/227 Jersey CHYNJ. 3,252,831 5/1966 Ragan 252/514 Primary Examiner-DouglasJ.Drummond .5 1 Attorney-Popper, Bain, Bobis & Gilfillan METALIZING MATERIAL 7 Chums 1 Drawing ABSTRACT: A metallizing composition for forming electri- U.S. l 252/514, cally conductive areas on dielectric materials, which areas I l7/227, 106/ 1 bond securely to the dielectric base materials, and which areas Int. I H0lb l/02, form secure bonds with conductive and mechanical at- B44d l/02 tachments, the composition being a mixture by weight of ap- Field of Search 252/514; proximately 63.7 percent gold, 32.3 percent palladium, 4.0

1 17/227; 106/ 1 percent silver.

Pd 29-34 70 I 4g Pd PATENIED SEP28 I97| on k. Yaw 3* 8 3 00 n INVENTOR SANDFORD S. COLE JR.

BY M: I We a A O NEYS BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates generally to metallizing compositions, and particularly to such compositions which form secure bonds when applied to dielectric basis, and form secure bonds with conductive and mechanical attachments such as, semiconductors, resistances, terminals, connectors and other such items ordinarily applied to printed circuits.

2. Prior Art 7,

The art of metallizing dielectric materials is highly developed. Conductive compositions of metals are ordinarily applied to dielectric materials, frequently ceramic. The

ceramic is then fired, the metallized coating is securely bonded thereto. The metallized coating does not always form a secure bond and the circuit pattern so formed may be broken, and may become inoperative. Usually noble metals are used, and sometimes mixtures or alloys thereof. The metals are prepared as a fine powder, and are suspended in an inert liquid medium, usually organic in character. The metallizing coating is applied to a dielectric substrate by painting, or screening or by other well-known techniques.

In addition to the problem of insecure bonding between the dielectric base and the metallized coating which results in detachment of the conductive coating, or its breaking, another troublesome problem arises. Certain mixtures of alloys of noble metals, when applied to a dielectric base and fired thereon, assume a rough texture characterized by fissures and porosity. It might be thought that the fissures and the porous character of the surface might enhance the bond that might be made on such surface, by providing an increased interface area for the solder, but such is not the case. Such metallized coatings, characterized by fissures and porosity are undesirable because their conductivity is reduced, and the mechanical strength of the coating is also reduced. the coating is also reduced. This last factor contributes towards the breakdown of the circuit.

Aside from the weakness of the bond that arises from fissures and porosity, some alloy compositions are incompatible with some solders, and the interface between such metallized coatings and attachments secured thereto by the use of solder is exceedingly weak and readily subject to detachment. Numerous mixtures of noble metals are known for metallizing. L. F. Miller authored TERNARY ALLOY ELECTRODE PASTES under date of July 8, 1968, which paper has been distributed by IBM as TR 22.654; he also delivered the article as a lecture at a packaging symposium in Los Angeles, California in Aug. of I968. In that lecture and in the publication, Miller refers to mixtures of gold, silver and palladium with other materials in a particular amount. Particularly percent silver is suggested but the bond secured between a composition with that amount of silver and a dielectric ceramic base, while adequate, does not have great strength.

Wagner US. Pat. No. 3,347,799 suggests a metallizing composition including two noble metals, gold and palladium, but does not suggest the inclusion of silver. Here again, the combination of gold and palladium as a metallizing composition, when limited strictly to the optimum range suggested by the inventor provides an adequate bond to a dielectric base and an adequate metallized coating to which attachments of various kinds may be soldered or brazed. Wagner suggests in addition to the optimum metallizing composition, there are other variant compositions that provide coatings which are at least workable. Hoffman U.S. Pat. No. 3,440,062 suggests a metallizing composition of gold with platinum or palladium and this too, forms adequate bonds to dielectric bases and an adequate base for soldering or brazing attachments. But here again, the interface of truly great strength between the substrate and the coming and the attachment is not achieved. The same is true in Hoffman, U.S. Pat. No. 3,385,799 where gold and platinum and gold and palladium in other proportions are suggested.

SUMMARY OF THE INVENTION It has been found that a mixture of gold, palladium and silver as a metallizing composition wherein the silver is present in the magnitude of one twenty-fifth to one-fiftieth of the combined weights of the noble metals; the gold and the palladium are present as metal powders in the range of 62-69 percent gold and 29-34 percent palladium; the remainder is not less than 2 percent nor more than 4 percent silver; this produces a metallizing composition which displays notable enhanced adherence to dielectric bases, and affords a coating to which adherence of conductive and mechanical attachments is notably enhanced. With this low percentage of silver, migration of silver in humid atr'nospheres is insignificant, and oxidation of palladium is inconsiderable. Noise effects are also drastically reduced. Thus, it is possible to produce printed circuits and the like of great strength, solderability, and durability to which strong and firm bonds of conductive and mechanical attachments are possible by solder.

The strength of the coating compositions adherence to the dielectric base is the result of the high density of the coating composition after firing, the initial absence of fissures and porosity, and the fact that the silver retards the oxidation of the palladium, for oxidation is a factor which contributes to the weakening of the interface bonds. As noted by Hoffman in U.S. Pat. No. 3,385,799, gold and palladium alone within the ranges herein set forth do not produce metallizing compositions which are satisfactory. It is the combination of a small amount of silver with the gold and platinum, within the ranges herein indicated which produces the optimum results herein described.

FIG. 1 is a diagrammatic representation of the critical range 0 metal powders in the composition; the equilateral triangle figure depicts each of the three metal powders in the range of percent, starting at the apex designated by the metal, ending at 0 percent at the opposite end of the altitude.

PREFERRED EMBODIMENT OF THE INVENTION Generally speaking, gold powders, palladium powders and silver powders having an average percent of less than 1 micron, with some possible inclusions of particles as large as 5 microns are prepared as a mixture within the following ranges: gold- 62-69 percent, palladium- 2934 percent and silver- 2IpeT-defif Numerous inertorganicl iquid vehicles are well known and available for metallizing compositions. Among those suitable is ethyl acetate. Others are pine oil; terpineols; ethyl, butyl, propyl, methyl, and higher aliphatic alcohols. The amount of liquid vehicle for the metal powders is not critical, but is largely dependent upon the degree of fluidity desired. Generally speaking, however, the metallizing composition may include up to 10 parts by weight to 1 part by weight of liquid vehicle. It is well known to add glass to the metallizing composition, where the coating is to be bonded to a ceramic base and so oxides are added to the vehicle. It has been found that the metallizing coating may consist of approximately 65.5 percent metal powders, approximately 23.9 percent organic vehicle and 10.6 percent oxides (the inorganic binder).

The oxide composition is somewhat critical. A mixture of oxides rather than frit is preferred. The oxides mixture percent is percent follows: l7-23 percent silicon dioxide, l-S percent boron trioxide, 40-50 percent lead oxide, 0-4 percent aluminum oxide and 20-40 percent bismuth trioxide. The oxide mixture is satisfactory without the boron trioxide, with a somewhat lessening of the adherence of the metallizing compound. As indicated by the percentage specified, the aluminum oxide may be altogether eliminated.

The metallizing compound, including the oxide, the metal powders and the vehicle are thoroughly mixed and form a suspension which is relatively stable for long periods of time, when applied to a ceramic base by painting. screening or other suitable manner, it is fired thereon and forms a hard. dense area strongly bonded to the ceramic base. Surface fissures and porosity are drastically reduced and solders are easily applied and form an excellent bond for attachments.

EXAMPLE 1 4.0 65.5 percent metal powder: (63.7 percent gold, 32.3 percent palladium, 4.0 percent silver) 23.9 percent organic vehicle (ethyl acetate) 10.6 percent oxide (Si0,20.6 percent; B,o, 2.2 percent; PhD-46.6 percent Al,O 0.6 percent; Bi,0,30.0 percent) EXAMPLE 2 2.0 65.5 percent metal powder: (65.0 percent gold; 33.0 percent palladium; 2.0 percent silver) 23.9 percent organic vehicle l0.6 percent oxide (Si,O 20.6 percent; B,O 2.2 percent; PhD-46.6 percent; A1,0,0.6 percent; Bi,O 30.0 percent) ln each of the examples the metal powders and the oxides were mixed and then the organic vehicle was added and thoroughly mixed with the powders to form a suspension which remains stable for months without substantial separation.

The l compound is then applied in any suitable manner to a ceramic base and is then fired. Firing is at a temperature of approximately 875 C. for approximately minutes in air whereupon the product is cooled.

in order to test the quality of the metallized areas, a copper ribbon of approximately 0.003 inches thick is soldered to the metallized surface and was subjected to a pull which was gradually increased to l4 pounds per linear inch. No examples of failure of bond occurred. Under greater stress, commencing at about l8 pounds per linear inch, failure did arise at the interface between the metallized coat and the ceramic base, and at the interface between the soldered connection of the ribbon. It is concluded that the bonds to the ceramic base and to the attachments are substantially equally secure. Within the ranges set forth, numerous additional examples are possible, all with substantially equally satisfactory results. The ranges set forth represent the preferred limits for a suitable metallized area. Beyond these ranges the instability of the attachments rapidly increase and are not considered to be suitable. percent When 4 metal powder mixture exceeds the ranges of 62-69 percent gold, 29-34 percent palladium, and 2-4 percent silver, the metallized areas, after firing, change in strength, porosity, solderability and adhesion.

Thus, less than 2 percent silver causes the formation of a surface percent that is strongly incompatible to solder. More than 4 percent silver causes a drastic reduction in adhesion of soldered attachments.

Less than 60 percent gold reduces aherence to a substrate, decreases solderability, and increased porosity. More than 69 percent gold does not change solderability but reduces adhesion strength and also increases porosity. 62 Less 3 29 percent palladium with 62 percent gold constant, and correspondingly larger amounts of silver,'causes no change'in solderability, but adhesion is reduced; also porosity is increased. More than 34 percent palladium, with gold percentage less than 62 percent, with silver constant in the range of 2-4 percent produces reduced solderability, reduced adhesion, and increased porosity.

It becomes apparent from a great number of tests that formulations having the least amount of porosity, the most satisfactory adhesion strength, and the best degree of solderability lie in the percentage range defined for preferred embodiments.

What is claimed is:

1. percent metallizing material comprising metal powder; and an inorganic binder; wherein the metal powder is approximately 6269 percent gold, approximately 29-34 percent palladium, and not less than 2 nor more than 4 percent silver.

2. The metallizing material according to claim 1 in which the inorganic binder is approximately l723 percent SiO 0-5 percent B,O

0- Opercent PbO 1-4 percent A1 0 2040 percent ago, 23.9 3. The metallizing material according to claim 1 constituting approximately 65.5 percent with approximately 23.9 percent of an inert organic vehicle, and approximately 10.6 percent of the inorganic binder.

4. The metallizing material according to claim I in an inert organic vehicle.

5. The metallizing material according to claim 2 in an inert organic vehicle.

6. A metallized article comprising a dielectric base, metallized areas fired thereon, the metallized areas comprising material according to claim 1.

7. A metallized article comprising a dielectric base, metallized areas fired thereon, the metallized areas comprising material according to claim 2. 

2. The metallizing material according to claim 1 in which the inorganic binder is approximately 17-23 percent SiO2 0-5 percent B2O3 40-50 percent PbO 1-4 percent A12O3 20-40 percent Bi2O3
 3. The metallizing material according to claim 1 constituting approximately 65.5 percent with approximately 23.9 percent of an inert organic vehicle, and approximately 10.6 percent of the inorganic binder.
 4. The metallizing material according to claim 1 in an inert organic vehicle.
 5. The metallizing material according to claim 2 in an inert organic vehicle.
 6. A metallized article comprising a dielectric base, metallized areas fired thereon, the metallized areas comprising material according to claim
 1. 7. A metallized article comprising a dielectric base, metallized areas fired thereon, the metallized areas comprising material according to claim
 2. 